<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let balance, phone, online;
        balance = 30
        phone = 0.1
        online = 0.3

        let PhoneTime
        PhoneTime = balance - phone - online * 30
        alert(`${PhoneTime}`)
    </script>




</body>

</html>